I am now seriously considering 7D + EF 24-70 F/2.8L USM.
Scrap that lens -- way too big and bulky. You'll curse it forever. The body with that lens mounted, won't fit into _any_ reasonable camera bag. Not even the bag I carried around Roma!
Yes, I have that lens. It takes excellent photos, and has fantastic depth-of-field control etc.. And it's a real pig to manage. I _never_ take it further than it can be carried by our automobile.
Get something smaller instead. I _highly_ recommend the 17-85 EF-S lens for this series of cameras. Sure, the optical quality is probably "only" double or triple that of your G11, nowhere near the 24-70 wide open, BUT.. it has image stabilization, is lightweight, covers the sweetest zoom range, and FITS in any camera bag.
When I travel the globe, I take the Canon body (D60, 20D, or now 40D), plus three lenses. Exactly which three varies from trip to trip, but I choose them from this pool:
10-22 EF-S
(fantastic for indoor use)16-35L (f2.8)
(my all-time favourite lens; dark/indoor uses)17-85 EF-S IS
(best all-rounder)24-104L IS (f4.0)
(decent mid-range zoom, but not wide enough)70-300 DO IS
(excellent and compact tele-zoom)70-200L IS (f2.8)
(HUGE lens, unbelievable image quality)(I do have other lenses too, but not for travel use).
Most of the time, it's the 16-35, 17-85, and 70-300.
Sometimes, I'll substitute the 24-105 for the 17-85, but it isn't quite wide enough for a lot of travel pics (esp. cities).
Still, to repeat,
get the 17-85 EF-S IS lens. And _only_ that lens. Then, 6 months from now, perhaps consider something different. But get used to things with that one lens to begin with.
Or, if you're suffering "L" envy, perhaps get the 24-105L IS instead, but it's really not wide enough to be the only lens in the kit.
Cheers